1. Field of the Invention
The present invention relates to a fuel cell system and, more specifically, to a fuel cell system configured to deal with its failure.
2. Description of the Related Art
A typical fuel cell stack is constituted as follows. First, an anode (fuel pole) and a cathode (air pole) are arranged on the respective surfaces of a proton exchange membrane, thereby forming a junction material. Second, this junction material is placed between two separators, whereby a single cell is formed. Finally, the multiple single cells are stacked.
Such a fuel cell stack produces water at its cathode (air pole) upon power generation. The part of this water soaks in the proton exchange membrane of each cell, then reaching the anode (fuel pole) side. Furthermore, in order to keep the wetness of the proton exchange membrane, a way to supply wet air (oxidant gas) to the cathode side is typically employed.
Because of the above water and wet air, gas such as fuel gas or oxidant gas flowing in the fuel cell stack contains a large percent of moisture, while the fuel cell stack generates electricity. Once the fuel cell stack stops the generation, the temperature of the gas is lowered so that the moisture in the gas condenses. Therefore, consider the fuel cell stack operates to generate electricity during any given period at low temperatures, for example, in winter or cold climate areas, and it then stops the operation. In this case, the moisture in the gas is prone to be frozen. Subsequently, if the fuel cell stack re-starts the operation, then its operating performance may be made worse.
In consideration of the above problem, a fuel cell system has been proposed in which moisture in the fuel cell stack is eliminated by scavenging the anode or cathode with air. An example of this fuel cell system is described in Japanese Unexamined Patent Application Publication 2001-351666.
This exemplified fuel cell system is provided with a communication path between its fuel gas path and oxidant gas path arranged upstream of the fuel cell stack. Furthermore, an open/close valve is installed in the communication path. When the system stops its operation, the open/close valve is opened. Simultaneously, an air pump supplies scavenging gas (dry air) to the cathode of the fuel cell stack through the oxidant gas path. Subsequently, the scavenging gas (dry air) reaches the anode of the fuel cell stack from the oxidant gas path through the communication path and the fuel gas path. Consequently, the moisture in the fuel cell stack is eliminated.
However, the above fuel cell system has the following disadvantage. Assume that the open/close valve of this system is improperly being opened during power generation. In this case, if the fuel gas path has higher pressure than the oxidant gas path across the opened open/close valve, then fuel gas, that is, hydrogen gas flows into the cathode side of the fuel cell stack. This may cause the deterioration of the fuel cell stack. Hence, a fuel cell system has been in demand that has an ability to determine easily whether the open/close valve fails or not.
Likewise, when cross leakage occurs between the anode and cathode sides of the fuel cell stack upon power generation, the fuel gas, that is, the hydrogen gas flows into the cathode side of the fuel cell stack. In this case, the fuel cell stack may also be deteriorated. Accordingly, a fuel cell system has been in demand that has an ability to determine easily whether or not cross leakage occurs between the anode and cathode sides of the fuel cell stack.
Taking the above demands into account, the present invention has been contrived. An object of the present invention is to provide a fuel cell system capable of determining easily whether or not any failure occurs in an open/close valve (air inlet valve) located in a communication path between a fuel gas path and oxidant gas path of a fuel cell stack. An additional object of the present invention is to provide a fuel cell system capable of determining easily whether or not cross leakage happens between the anode and cathode sides of a fuel cell stack.